Mysterious $100 'Supernote' Counterfeit Bills Pop Up Worldwide

An underground counterfeiting operation appears to continue with $100 'supernote' bills popping up worldwide, while questions remain about possible North Korean ties to the phony bills.

The 'supernote' appears to be made from the same cotton and linen mix that distinguishes U.S. currency from other currency. It even has watermarks visible from the other side of the bill, colored microfibers woven into the substrate of the banknote and an embedded strip, barely visible, that reads USA 100 and glows red under ultraviolet light.

The secret operation, stumping officials worldwide, could be the "most sophisticated counterfeiting operation in the world," former congressman James Kolbe told McClatchy Newspapers.